1. Field of the Invention
The present invention relates to a method for grinding the traction surface of a continuously variable transmission (CVT) disk of a half-toroidal type.
2. Description of the Related Art
Recently, the traction surface of a half-toroidal CVT disk used as a continuously variable transmission of a car has been worked or ground by a grinding machine.
The grinding machine used for such grinding operation includes a cylindrical grinding disk of a plane type and a grinding machine of an angular type. In the plane type grinding machine, a swing angle xcex81 is set at 90xc2x0 and, in the angular type grinding machine, a swing angle xcex81 is set at 60xc2x0; and, a grindstone, which is mounted on the rotary shaft of the grinding machine, is slidably disposed in such a manner that it can cut in a direction perpendicular to the rotary shaft of the grindstone (xcex81=90xc2x0) or at an angle (xcex81=60xc2x0).
In the grinding machine, a work to be ground is held on an XY table. The XY table has not only the function of an X table to slide the work in an X direction but also the function of a Y table to slide the work in a Y direction. The X direction is the sliding direction of the work in the diameter direction thereof, whereas the Y direction is the sliding direction of the work in the rotation axis direction thereof.
In order to be able to carry out both of the X-table and Y-table functions with respect to the upper surface of the XY table, two structural elements required to fulfill their respective functions are piled up in two layers, and they are respectively superimposed on a spindle on the XY table side.
Also, referring further to a table for holding a work as other structural element than the XY table, there has been applied by the present applicants, a grinding machine comprising a swing table which can be slided in a direction perpendicular to the cutting direction of a grindstone (Japanese Patent Unexamined Publication No. 11-226870 of Heisei).
By the way, in the above-mentioned conventional grinding machines, there is found a problem that an actual machining allowance and an apparent machining allowance are different from each other. Also, there is raised another problem as to a grindstone interference diameter. That is, as shown in FIGS. 2A and 2B, when a grindstone 26 is outside butted against the grinding surface (that is, the surface to be ground) of a work 28, if the actual machining allowance is expressed by t, then the following relationships hold between the actual machining allowance t and apparent machining allowance txe2x80x2 (that is, a dimension over which the grindstone 26 advances from the outside of the machining allowance to a traction surface when it is completed):
t=txe2x80x2xc3x97cos(xcex81+xcfx891)xe2x80x83xe2x80x83Expression 1
where, xcex81: spindle swing angle (an angle formed between a direction extending along the cutting direction of the grindstone 26 and a direction extending in parallel to the mounting surface of the work 28), and
xcfx891: Arc sin((xcfx86xe2x88x92pcd)/(rxe2x88x92t))xe2x80x83xe2x80x83Expression 2.
Here, pcd expresses a radius which extends from the center of a curved surface of the traction surface of the CVT disk when it is completed to the center of the work 28 (PCD expresses the diameter of pcd), xcfx86 expresses the outer peripheral radius of the work 28, and r expresses the radius of the curved surface of the traction surface of the CVT disk when it is completed.
Also, as shown in FIGS. 3A and 3B, when the grindstone 26 is inside butted against the grinding surface of the work, the following relationships hold between the actual machining allowance t and apparent machining allowance txe2x80x2:
t=txe2x80x2xc3x97cos(xcfx802xe2x88x92xcex81xe2x88x92xcfx892)xe2x80x83xe2x80x83Expression 3,
xcfx892: Arc sin((h1xe2x88x92h2)/(rxe2x88x92t))xe2x80x83xe2x80x83Expression 4.
Here, h1 expresses a height which extends from the bottom surface of the work 28 to the center of the curved surface of the traction surface of the CVT disk when it is completed, and h2 expresses the dimension of the height of the work 28.
As can be seen from the above-mentioned expressions, in both cases in which the grindstone 26 is outside and inside butted against the grinding surface of the work 28, a cutting magnification txe2x80x2/t provides a value larger than 1, which means that the apparent machining allowance is larger than the actual machining allowance and, therefore, there is raised a problem that the cutting time of the grindstone 26 is made long.
Also, as the swing angle is made larger, the grindstone interference diameter must be reduced accordingly. Otherwise, there is caused interference in the outer peripheral portion of the disk with respect to the grindstone and, therefore, the outer peripheral portion of the disk is ground not in a linear contact manner but the work 28 is ground in a surface butting manner, which results in the dull ground shape.
Accordingly, if the grinding operation of the work 28 is executed by the grindstone 26, then the outside dimension of the grindstone 26 becomes small with the grinding of the work 28. Thus, if the grindstone diameter that can be used is small, then a spindle, on which the grindstone 26 is mounted, must be rotated at a high speed in order to gain the grindstone peripheral speed. In this case, the diameter of the shaft of the spindle becomes finer or smaller according to the dimension of the small grindstone diameter, thereby causing the rigidity of the spindle shaft to lower. Therefore, if the grindstone 26 is rotated at a high speed in order to enhance the grinding or working efficiency, then there is raised a fear that the rigidity of the spindle shaft can be made insecure. This problem will a rise not only in a case in which the grindstone diameter is reduced as it is used but also in a case in which the diameter of the grindstone 26 is previously set small.
Also, in a case in which the diameter of the grindstone 26 is previously set small, the usable range of the grindstone 26 is small and, therefore, the frequency of replacement of the grindstone 26 increases. This requires more time for replacement of the grindstone 26, which reduces the operating time of the grinding machine. Thus, the productivity of the work 28 cannot be enhanced, which is a disadvantage in the working or grinding cycle.
Further, if the grindstone diameter used is small, the number of abrasive grains of the grindstone surface actually used in the working or grinding operation is small. This reduces an interval in which the clogged grindstone is dressed, which also provides a disadvantage in the working or grinding cycle.
In addition, in a case in which a grindstone diameter used is equal to or less than a given value, it is difficult to structure a grinding machine. That is, a bracket for embracing the spindle and a grindstone base for carrying the bracket thereon must have mass and size equal to and larger than a given value regardless of the grindstone diameter and, therefore, it is difficult to structure a grinding machine in which only the grindstone diameter is small.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional method for grinding the traction surface of a half-toroidal CVT disk. Accordingly, it is an object of the invention to provide a method for grinding the traction surface of a half-toroidal-type CVT disk in which the disk can be ground or worked within the proper range of spindle swing angles and the diameter of a grindstone is set equal to or larger than a given value.
In attaining the above object, according to the first aspect of the invention, there is provided a method for grinding a traction surface of a half-toroidal CVT disk, including the steps of:
preparing a grinding machine including a hold mechanism holding the half-toroidal CVT disk having a given machining allowance; and a machining mechanism including a tool for grinding the half-toroidal CVT disk, the grinding of the grinding machine being performed in a state that one of the half-toroidal CVT disk and the tool is inclined at a predetermined angle with respect to the other; and
setting a cutting angle, which is an angle to be formed by the cutting direction of the tool with respect to the axis of the half-toroidal CVT disk, in the range of xc2x115xc2x0 with respect to the angle that a first cutting magnification at the time of that the tool contacts with an outer periphery position of the traction surface is substantially equal to a second cutting magnification at the time that the tool contacts with an inner periphery position of the traction surface, each of the first and second cutting magnifications being a ratio of an apparent machining allowance to the given machining allowance.
With the first aspect of the invention, since the cutting angle of the tool is set in the range of xc2x115xc2x0 with respect to the angle that makes the cutting magnification smallest, the apparent cutting magnification does not become so large but can be controlled down into a small range. Thus, this makes it possible to shorten the grinding operation time.
According to the second aspect of the invention, there is provided a method for grinding a traction surface of a half-toroidal CVT disk, including the steps of:
preparing a grinding machine including a hold mechanism holding the half-toroidal CVT disk having a given machining allowance; and a machining mechanism including a tool for grinding the half-toroidal CVT disk, the grinding of the grinding machine being performed in a state that one of the half-toroidal CVT disk and the tool is inclined at a predetermined angle with respect to the other; and
setting a swing angle, which is an angle to be formed by the rotation axis of the tool with respect to a surface perpendicular to the axis of the half-toroidal CVT disk so that an angle difference between a cutting angle, which is an angle to be formed by the cutting direction of the tool with respect to the axis of the half-toroidal CVT disk, and the swing angle is 15xc2x0 or less.
With the second aspect of the invention, because angle differences between the swing and cutting angles of the tool can be set individually at 15xc2x0 or less, it is possible to select the swing angle of the tool that can made the grindstone interference diameter large. And, since the above angle differences are equal to or less than 15xc2x0, a load to be applied to the tool in the thrust direction thereof can be prevented from being large, which can prevent an inconvenience that a thrust load can be applied to the tool to thereby break the tool or worsen the grinding accuracy of the tool.
In this case, if the cutting and swing angles are set properly, compatibility between the cutting magnification and tool diameter can be secured. Due to this, the work grinding performance of the tool can be enhanced comprehensively.
According to the third aspect of the invention, there is provided a method for grinding a traction surface of a half-toroidal CVT disk, comprising the steps of:
preparing a grinding machine including a hold mechanism holding the half-toroidal CVT disk having a given machining allowance; and a machining mechanism including a tool for grinding the half-toroidal CVT disk, the grinding of the grinding machine being performed in a state that one of the half-toroidal CVT disk and the tool is inclined at a predetermined angle with respect to the other;
determining the maximum diameter of the tool in the range of 0.9 times to 0.5 times an interference grindstone diameter, the interference grindstone diameter being calculated from a dimension between the center of curvature of a curved surface of the traction surface of the half-toroidal CVT disk and the rotation center of the half-toroidal CVT disk, the dimension of the radius of curvature of the traction surface, the dimension of the outer peripheral diameter of the traction surface, and a swing angle, which is an angle to be formed by the rotation axis of the tool with respect to a surface perpendicular to the axis of the half-toroidal CVT disk; and
setting the swing angle so that an angle difference between a cutting angle, which is an angle to be formed by the cutting direction of the tool with respect to the axis of the half-toroidal CVT disk, and the swing angle is 15xc2x0 or less.
With the third aspect of the invention, because the interference diameter of the tool is obtained from the swing angle and the dimension of the work and the diameter of the tool is set in the range of 0.9 times to 0.5 times the grindstone interference diameter, the diameter of the tool to be used actually can be made largest in its allowable range. This makes it possible to shorten the grinding operation time, and provides a proper grinding which improves the efficiency of the grinding operation and the accuracy thereof. Also, the grinding operation can be carried out in such a manner that there are removed factors causing the poor surface quality such as the dull generator shape, re-grinding and the like.
Also, since a sufficient usable range of the tool can be secured, it is possible to reduce the frequencies of dressing and replacement of the tool. This can increase the time ratio of the actual grinding operation to the general grinding operation, so that the grinding performance of the grinding machine can be enhanced.
The present disclosure relates to the subject matter contained in Japanese patent applications No. Hei.10-122294 filed on May 1, 1998 and No. Hei. 11-011676 filed on Jan. 20, 1999 which are expressly incorporated herein by reference in its entirety.